This invention relates to furnaces. This invention is concerned with furnaces commonly called bale-out in which the metal is melted in a crucible and then removed by a ladle dipped into the melt. However, this invention could be applied to other types of furnaces which have removable crucibles, or which are tilted to pour the molten metal into a ladle or the like. Additionally, this invention is concerned with furnaces which are fuel-fired, that is not electric furnaces.
Previously, the combustion air for a furnace burner has either been delivered directly to the burner at ambient temperatures or has been pre-heated by heat exchange with the products of combustion. In the case where pre-heating has occurred this usually involves passing the combustion air through a jacket surrounding the refractory lining of the furnace. The lining is quite heat conductive and therefore a large proprortion of the heat used for preheating the combustion air is heat that could have been used for heating the metal. Accordingly, although the efficiency of the furnace is increased on the one hand by pre-heating the combustion air, the efficiency is simultaneously decreased by the utilisation of useful heat to pre-heat the air.
It is an object of the present invention to improve the efficiency of the furnaces as aforementioned by providing an improved furnace construction in which combustion air for a furnace burner is headed in two stages by waste heat only.